Recording cassette audio through a USB port

Yes, anything that will connect an audio input into

See: this help page

Connect your cassette player like an external microphone. Either plug an audio interface (like an Apogee Jam or iMic) into the USB port or an input splitter into the headphone jack. You can use the headphone jack, if it is a 3.5 mm headphone jack with support for Apple iPhone headset with microphone. Then the splitter will turn it into two audio ports, one for the audio input and one for audio output, like this: 3.5mm Audio Jack to Headphone and Microphone U Splitter Converter Adaptor: Amazon.co.uk: Computers & Accessories

The iMic used to be the cheapest audio interface for the USB port, but it is no longer sold. Apogee interfaces have an excellent audio quality and less latency, but are more expensive.

Thanks léonie, the crux of my query I guess - is an audio interface needed?

Only your ears can tell you. It will depend on the quality of the amplifier in the device, where you are playing the cassette. If that sounds good, when you connect a decent headphone to the player, an input splitter cable for the headphone port should suffice.

I did it that way, maybe 12 years ago.

I have never used Garageband. When I did it you needed/wanted to do the audio-in setup with: Set up audio devices on iMac (Mid 2014) and later - Apple Support